Locomotives supplied by the assignee of the present invention include a diesel engine that drives an alternator for producing electrical power. The electrical power from the alternator is conducted to traction motors located beneath a platform of the locomotive. The traction motors drive wheels through a gearbox for propelling the locomotive along the tracks. A similar drive system is used for other off-highway vehicle applications such as for mining vehicles.
FIG. 1 illustrates a portion of the under-platform equipment used in a locomotive including a traction motor 10, gearbox 12 and axle 14. The motor 10 includes a frame 16 assembled from several separate members including a stator housing 18, a connector end plate or frame head 20, and a drive end plate 22. Axially extending through the motor frame 16 is a motor shaft 24 that is connected to a pinion gear 26 within the gearbox 12. The pinion gear 26 drives an axle gear 28 connected to the main axle 14 for powering the drive wheels 30 of the locomotive.
Motor 10 includes a stator portion 32 and a rotor portion 34. The motor 10 is cooled by a flow of cooling air 36 (indicated by arrows) received into the motor 10 through a duct 38. The cooling air 36 is directed through cooling passages 40 formed in the stator portion 32 and the rotor portion 34 and exits the motor 10 through a plurality of windows or access openings 42 formed in the frame head 20. It will be appreciated that other arrangements of the above-described components may be found on various models of locomotives.
The stator portion 32 includes conducting elements 44 such as stator coils for conducting electricity to generate the magnetic field for powering the motor 10. Other types of electro-dynamic apparatus may include other types of conducting elements, such as the bus rings and associated connectors found on an alternator. The conducting elements 44 include a conductor of electricity encased in insulating material for isolating the electricity from the electrical ground of the motor frame 16. The insulating material may take any of several forms known in the art, such as tape/varnish systems or powder coat systems. Portions 46 of the conducting elements 44 are located within the motor frame 16 proximate the access openings 42 and are thus subject to damage from the impact of debris that is propelled by the wheels 30 and passes through the access openings 42. These portions 46 of the conducting elements 44 are also exposed to the accumulation of moisture and occasionally grease that may escape from the gearbox 12. These accumulations of dirt and moisture on the insulation provide a pathway for electricity causing a phenomenon referred to as “tracking”. Small openings may develop through the insulating material to the underlying conductor as a result of the stress of operation, the impact of debris, or the presence of small pinholes produced during the application of a powder coat insulation system. As the insulating material degrades through continued exposure to the elements through the access openings 42, the amount and intensity of tracking will increase, eventually leading to a short circuit between the conducting element 44 and the motor frame 16 and the failure of the motor 10. Such failures are very costly because they degrade or prevent the operation of the locomotive and they necessitate the complete disassembly of the motor 10 for repair.
A similar concern exists for any electro-dynamic apparatus wherein insulated conducting elements are exposed to an environment where dirt and moisture may accumulate on electrical insulation. For example, the alternator of a locomotive is air-cooled and includes conducting elements that are exposed to the flow of cooling air that may be carrying dirt and moisture. Manufacturing porosity and/or surface flaws induced by operating stresses and particle impact may combine with the accumulated dirt and moisture and lead to an increase in tracking and eventual failure of the apparatus.